1. Field of the Invention
The present invention relates to a demodulator for suppressed carrier biphase PSK signals.
More in particular, the present invention relates to a demodulator for digital signals modulated in biphase PSK with suppressed carrier of the kind utilized in the transmission of digital messages on a radiobroadcast channel, in particular stereo radio broadcasting, known as "radiodata".
2. Description of the Prior Art
Recently a data transmission system has been developed known as "radiodata" in which a data transmission is performed in the frequency modulated channels of radio broadcast utilizing an auxiliary carrier at the frequency of 57 KHz corresponding to the third harmonic of the pilot carrier of the conventional stereo transmissions according to the C.C.I.R. standards, corresponding to 19 KHz. The recovery of the information transmitted with the system in question is relatively complex, as it is necessary to reconstitute the carrier at 57 Khz which is suppressed during transmission.
Several systems have been proposed for obtaining demodulation of this kind of signal: see for instance the article "IL RADIODATA: nuovo servizio in radiofonia MF" by Cominetti, Elettronica e Telecomunicazioni No. 2, 1985; "Specifications of the radiodata system RDS for VHS/FM Sound Broadcasting" - European Broadcasting Union, technical Center, Brussels, March 1984; and, "Digital Communications by Satellite", Vijay K. Bhargava et al, John Wiley & Sons, N.Y.
The aim of the present invention is to provide a demodulator and decoder of signals for transmissions of the "radiodata" kind with improved features with respect to the known art and that can be realized with purely digital techniques that can be integrated at low cost, especially in an integrated circuit for performing a number of other functions.